The technical field of this invention is cleaning apparatus for rinsing and drying containers and carriers used to hold and process semiconductor wafers, substrates, flat panel displays and other flat media requiring low contamination levels.
Flat media, such as silicon or other semiconductor wafers, substrates, photomasks, flat panel displays, data disks, and similar articles require extremely low contamination levels. Even minute contaminants can cause defects. Accordingly, it is necessary to maintain a high level of cleanliness during all or nearly all stages of production of these types of flat media. The flat media described may be referred to below as xe2x80x9cwafersxe2x80x9d, although it will be understood that xe2x80x9cwafersxe2x80x9d means any form of flat media.
Wafers are typically processed in batches. For example, in manufacturing semiconductor chips, for use in computers, telephones, televisions, and other electronic products, silicon wafers will undergo many batch processing steps, such as oxidation, photolithography, diffusion, chemical vapor deposition, metallization and etching. Batch handling may occur throughout the entire production process, or for one or more processing steps or related handling operations. Batch processing of this type almost always utilizes some type of carrier or container to hold the wafers being processed.
A wafer carrier or container holds a group of wafers. The wafer carriers can be of various designs, and are more specifically referred to as a wafer boat. In many applications, they are made of a suitable polymeric material, e.g., polypropylene or TEFLON(copyright) fluoropolymer. The sides and sometimes the bottom of the wafer boat have receiving slots formed to receive and hold the wafers in a spaced array with the faces of the wafers adjacent to one another. Typically, the central axes of the wafers are aligned. The wafers are slid into the carrier or container, such as from the side or above, and are removed by sliding them outwardly. The receiving slots are shallow so that the wafer is engaged only at the peripheral edges and along a thin marginal band extending inwardly from the periphery.
Wafer carriers can also be provided in the form of a protective case or box in which the wafers are held and are sealed against contamination during travel within the processing facility. Wafer carriers of this type are frequently designed to hold a wafer boat having a complementary design. The complementary relationship of the protective wafer carrier box and the wafer carrier boat allow the boat and supported wafers to be fully enclosed and securely held in place during transport. The term xe2x80x9ccarrierxe2x80x9d referred to below means a carrier, a container, with or without a lid, or a wafer boat.
At certain stages in the manufacturing process, the wafer carriers must be cleaned. Cleaning them is difficult because they typically have features which include slots, grooves or apertures, and inside corners. These difficulties are made worse by the extremely low contamination levels which are required for processing the wafers.
Accordingly, cleaning of wafer carriers remains a difficult, time consuming and relatively costly procedure. In addition, the carriers will often become contaminated with photoresist, a viscous sticky material used in manufacturing various semiconductor products. Photoresist can be especially difficult to clean away. Sticky-back labels, fingerprints, dust, metal particles and organic chemicals, may also contaminate the wafer carriers.
Various machines have been made and used for cleaning wafer carriers. In these machines, the carriers are mounted on a rotor and spin within a chamber, while cleaning solutions are sprayed onto the carriers. The spinning movement minimizes process time and also helps in drying the carriers. In certain applications, surfactant has been introduced and mixed with de-ionized water, at a concentration of approximately 1:10,000. Used in this way, the surfactant acts as a wetting agent which helps to remove only loosely adhered particles. The surfactant is used only once and then discarded as waste. While this use of surfactant has improved cleaning performance, it has been largely ineffective in removing contaminants such as photoresist, labels, and fingerprints.
Accordingly, it is an object of the invention to provide an improved machine for cleaning carriers and containers for flat media.
In a first aspect of the invention, an apparatus for cleaning flat media carriers includes a rotor rotatably mounted within a chamber. Nozzles within the chamber are arranged to spray a mixture of water and a detergent or surfactant on to carriers supported on the rotor. A reclaim tank is connected to the chamber, to collect and recycle the water and surfactant mixture. The mixture has a concentration of surfactant sufficiently high to remove contaminants such as photoresist, labels, and fingerprints.
In a second aspect of the invention, used mixture of water and surfactant is pumped through a filter before it is reused. Filtering the used mixture allows it to be re-used many times, without significantly reducing the cleaning effectiveness of the machine.
In a third aspect of the invention, the water and surfactant mixture is prepared in a mixing tank linked to the reclaim tank and to some of the nozzles. The mixing tank facilitates achieving the desired concentration of surfactant in the surfactant and water solution and provides a reservoir for the solution.
In a fourth aspect of the invention, a diverter valve diverts the run-off from the chamber to the reclaim tank, when the water and surfactant solution is sprayed within the chamber. The diverter valve diverts the run-off from the chamber to a waste drain during the parts of the cleaning cycle when no surfactant is used.